Passenger-side airbag modules are customarily positioned behind the instrument panel in front of the location of a seated passenger. The module is normally in the form of a trough which encloses the folded airbag (or "cushion pack"). A gas generator, or inflator, is associated with the module. In the event of a crash of sufficient magnitude, a sensor activates the inflator, filling the airbag. The expanding airbag bursts through a door in the instrument panel in order to cushion the impact of the passenger's body.
Because the airbag module is mounted closely adjacent the normally flexible instrument panel, it creates the risk of a head impact injury in the event of crashes of insufficient magnitude to activate the inflator. As a result, there is in effect Federal Motor Vehicle Safety Standard 201. This standard requires that an automobile instrument panel on the passenger side properly absorbs impact energy in the head impact region. Compliance with this standard becomes more difficult in view of the placement of the airbag module which adds rigidity.
That part of the airbag module which mostly affects compliance with FMVSS 201 is the reaction canister which houses the folded airbag. This canister is normally in the form of a trough having first and second side walls interconnected by first and second end walls which enclose the folded airbag and form an open mouth adjacent the instrument panel. These walls must be strong enough to support the airbag during deployment when airbag pressures are high. Nevertheless, they must be weak enough to collapse and absorb energy upon head impact in the absence of airbag deployment. The required energy absorption of the side walls is dependent upon the instrument panel and its ability to absorb some of the energy. In some instances the instrument panel will absorb all or most of the impact energy. Under other circumstances, however, the side walls must absorb nearly all of the energy--requiring as much as 2 inches of crush or deflection to minimize deceleration forces.
Two basic types of airbag module housings are in common use, steel stamped housings and extruded aluminum housings. Steel stamped side walls are usually perforated, or formed in special ways to make them more crushable. Aluminum extruded housings are usually perforated or include special geometry making them more deformable. Extruded aluminum housings are particularly popular because they are lightweight and many structural features can be incorporated in the extrusion. Typically, extruded housings are of a one piece design including an inflator housing joined to a pair of side walls which form the trough-shaped reaction canister. End plates are added to such an extrusion to complete the module.
One problem which is introduced by such a one piece extrusion relates to wall thickness. A typical extruded housing has a minimum wall thickness of 0.090 inch. This thickness limitation is due to the size of the extruded shape and is required to maintain dimensional stability during the extrusion process. In view of this limitation, it has been necessary in the past to perforate the side walls to weaken them and allow them to be crushed more easily. This has introduced an additional step in the manufacturing process which it would be desirable to eliminate.
A second problem arises from the fact that, in certain inflator housing constructions, gas exit holes must be punched, or otherwise formed, in the inflator housing to permit gas to flow into the reaction canister to inflate the airbag. The presence of the integral rigid reaction canister side walls interferes with the tool access required to produce the gas exit holes. Furthermore, since they are rigid one piece extrusions, it is sometimes necessary to provide special restraint fixturing in order to assist in screw positioning during attachment of the end plates and mounting to the vehicle structure.
Accordingly, it is a primary object of the present invention to provide an airbag module having an improved ability to meet the required head impact safety standards. Another object is to provide such module having thinner side walls, improved tool access for forming gas exit holes, and eliminating the need for special restraint fixturing. The manner in which these and other objects are achieved will be apparent from the following description and appended claims.